Two stage vacuum pump



TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet of'4 HELMUT BODE RUDOLFBRINKMANN ATTORNEY April 15, 1969 H. 8055 ETAL 3,438,570

TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet 9 of 4 FIGURE 3 HELMUTBODE RUDOLF BRINKMANN BY @375 )W ATTORNE Y April 15, 1969 BODE ErAL3,438,570

TWO STAGE VACUUM PUMP Filed Aug. 18, 1967 Sheet 4 of 4 HELMUT BODERUDOLF BRINKMANN BY fa ATTORNEY United States Patent 0 54, Int. Cl. F04c23/00, 29/02 US. Cl. 230-158 9 Claims ABSTRACT OF THE DISCLOSURE A twostage vacuum pump includes an outer housing consisting of a cup-shapedmember defining one end wall and the peripheral side Walls, and aclosing end wall which may be integral with a driving motor housing. Thetwo pump stages are side-by-side within the housing, each stageincluding a cylinder defining a cylindrical pumping chamber withsuitable inlet and outlet ports, and a cylindrical rotor eccentricallymounted within the chamber and provided with three radial slots foraccommodating sliding vanes. The stages are separated by a partition inthe form of a circular plate which is sealed with respect to the housingside walls by a peripheral O-ring, defining two housing chambers. Therotors are mounted on a common shaft which passes through the partition;and a passage through the partition communiactes the two stages. Each ofthe stage cylinders is mounted within its respective housing chamber todefine an annular space between the cylinder and the housing. Thepartition is provided with a passage communicating the second stageinlet with the annular space surrounding the first stage, whereby thisspace is maintained at the inlet pressure of the second stage defining avacuum jacket chamber for the first stage. The peripheral space betweenthe second stage cylinder and the housing wall defines an oil reservoir;and a controlled fiow passage in the cylinder provides for oil flow fromthe reservoir into the second stage pumping chamber. The opening of thejacket chamber passage is positioned in a second stage pumping chamberso that, when the pump is shut down without venting, the oil in thesecond stage chamber will flow through this passage into the jacketchamber rather than into the first stage pumping chamber; and thisjacket chamber is large enough to accommodate all of the oil which mightotherwise be sucked into the first stage resulting in undesirablecontamination.

Background of the invention This invention relates to a two stage vacuumpump, and more particularly to a rotary, mechanical, oil-sealedseries-connected pump.

For obtaining of near-perfect vacuum, two stage pumps are desirable; andthe effective sealing of the pump structure to prevent leakage is anever present problem. Another problem with pumps and pump systems, wherean oil-sealed pump is employed, is to prevent back-up of oil into thefirst or low pressure stage or into the system being pumped, should thepump be shut down without venting. It is, of course, undesirable to havethis oil flow back into the vacuum system, and it is also particularlyundesirable to have the oil flow back into the first stage tocontaminate this stage, since this necessitates considerable pumpingdown of the first stage before ultimate vacuum is obtained.

An object of this invention is to provide an improved structure for atwostage, oil-sealed vacuum pump.

3,438,570 Patented Apr. 15, 1969 A further object of the invention is toprovide a two stage pump in which the operating elements thereof aremore. effectively sealed against leakage than pumps of prior practices.

A'further object of this invention is to provide a two stage oil-sealedvacuum pump in which back-up of the oil into the low pressure stage isprevented.

Summary of the invention The above objects are accomplished by a pumpstructure including a housing having an internal partition defining twochambers. First and second pumping stages are mounted respectively inthe two chambers, each of the stages being mounted to define an annularspace between the outer walls of the pump stage cylinders and thehousing wall. The annular space surrounding the second or high pressurestage defines an oil reservoir chamber; and a metering passage providesfor flow of oil into the second stage pumping chamber. The annular spacesurrounding the first or low pressure stage is communicated, by apassage in the partition, with the second second stage inlet to define avacuum jacket chamber for the first stage. The vacuum jacket chamber andcommunicating passage also serve as an oil trap chamber for receivingoil from the second pumping stage which seeks to flow back into thefirst stage when the pump is shut down.

Brief description of the drawings FIG. 1 is a sectional view of a twostage vacuum pump according to the invention, the section being taken ina vertical plane through the axis of the rotors;

FIG. 2 is a transverse sectional view through the first pumping stage,taken along the line 22 of FIG. 1 looking in the direction of thearrows;

FIG. 3 is a transverse sectional view through the second pumping stage,taken along the line 33 of FIG. 1 looking in the direction of thearrows; and

FIG. 4 is a fragmentary sectional view taken along the line 44 of FIG. 3looking in the direction of the arrows.

Description of the preferred embodiment Referring to the drawings, a twostage vacuum pump according to the present invention includes a housingdefined by a cup-shaped member defining one end wall 11 and a peripheralwall which will be referred to as the side wall or side walls 12. Thecup-shaped member is secured, by any suitable means, to a plate memberwhich defines the opposite end wall 13 of the pump housing, and whichalso may be the common end wall of an adjacent housing containing amotor for driving the pump. The end wall 13 includes an opening withinwhich is mounted a bearing 15 for rotatably supporting a shaft 16, whichextends through the end wall 13 and into the pump housing to a pointadjacent the opposite end wall 11. This shaft 16 may be an extension ofthe drive shaft of a motor which is mounted on the opposite side of theend wall 13. A suitable rotary seal 17 may be provided to seal the shaftopening through the end wall 13.

The pump housing is provided with an intermediate partition 18, in theform of a circular disc or plate, which is disposed parallel to the twoend walls. This partition is provided with a peripheral annular groovefor retaining a resilient seal gasket such as a rubber O-ring 19. Thehousing side wall 12 is provided with an internal, integral annular rib20 defining an annular shoulder facing toward the end wall 13. The innerdiameter of the rib 20- is slightly larger than the outer diameter ofthe partition 18, so that the partition is relatively closely receivedwithin the rib 20; and the O-ring 19 bears against the shoulder 3 toprovide the desired sealing between chambers 21 and 22 in the pumphousing defined by the partition 18 on the left and right sides thereof,respectively, as viewed in FIG. 1.

As best seen in FIGS. 1 and 2, the first stage of the vacuum pump ismounted within the chamber 21, and includes a stage housing or cylinder25 supported within the chamber in a manner to define an annular spacebetween the periphery of the stage cylinder and the housing side walls12. The first stage cylinder 25 is a disc-like member having parallelend walls which are dimensioned for a close fit with the inner surfaceof the end Wall 11 and the confronting parallel surface of the partition18. The rotor is provided with a transverse cylindrical bore 26, whichdefines, with the closing walls, a first stage pumping chamber; and acylindrical rotor 27, of lesser diameter than the bore 26, is mounted onthe shaft 16 for rotation therewith by means of a key 28. The rotor ispositioned relative to the chamber so that the axis of rotation of therotor is eccentric relative to the axis of the cylindrical chamber, andthe rotor is tangent to the chamber at the upper periphery thereof asviewed in the drawings. The axial dimension of the rotor issubstantially the same as the distance between the cylinder closingsurfaces of the end wall 11 and partition 18, the tolerances being suchas to provide effective sealing aided by a lubricating and sealing oilas will be described. The rotor 27 is provided with three radial slots,for accommodating sliding vanes 29 which seal against the cylindrical-wall and the end walls of the pumping chamber 26. The cylinder, rotor,and vanes then define three separate chambers around the periphery ofthe rotor which serve to pump the fluid from the intake port to thedischarge port of the pumping chamber.

As best seen in FIGS. 1 and 3, the second or high pressure stage of thepump is mounted Within the chamber 22 between the partition 18 and theend wall 13. The structure of the second stage is generally identical tothat of the first stage, the rotors and vanes being identical andinterchangeable. The second stage also includes a stage housing orcylinder 31 which is a disc-like member having parallel end walls whichare dimensioned to engage the confronting parallel surfaces of thepartition 18 and end wall 13 in sealing relation; and this cylinder 31is positioned within the chamber 22 to define an annular space betweenthe periphery of the cylinder and the housing side Walls 12. Thecylinder 31 is provided with a cylindrical bore 32 which defines, withthe closing wall surfaces, the second stage pumping chamber. Acylindrical rotor 33 is mounted for rotation on the shaft 16 by means ofa key 34; and this rotor is eccentrically mounted within the bore 32 inthe same manner as the first stage rotor 27. The rotor 33- is alsoprovided with equally spaced radial slots for accommodating slidingvanes 35 which are dimensioned to seal against the cylindrical and sidewalls of the second stage pumping chamber.

It may be stated, so far as assembly of the pump is concerned, that theabove-described second pumping stage, partition 18, and first pumpingstage might be assembled to the end wall 13, with suitable dowels 38 toassure proper alignment of the parts. The housing member defining theend wall 11 and side walls 12 might then be suitably secured to the endplate 13.

As best shown in FIG. 1, the end wall 11 is provided with a chamber 41which defines an intake chamber for the pump and which may be connectedto the system to be evacuated by suitable tub-ulation not shown. The endwall 11 also includes an inlet passage 42 which communicates with aninlet passage 43 in the first stage cylinder 25. An inlet port 44 in thefirst stage cylinder communicates the inlet passage 43 with the firststage pumping chamber 26; and the fluid withdrawn from these passages bythe first stage rotor 27 is pumped through the chamber to the firststage discharge passage 45, the

4 rotor being driven in a clockwise direction as viewed in FIG. 2.

The first stage discharge passage 45 is communicated with the secondstage inlet passage 47 by means of a transfer passage 46 in thepartition 18. The inlet passage 47, in the second stage cylinder 31, asbest seen in FIG. 3, communicates with the second stage pumping chamber32 through an inlet port 48; and the fluid withdrawn from the inlet portis pumped around the rotor 33 to the second stage discharge passage 49in the cylinder 31, the rotor 33 also being driven in a clockwisedirection as viewed in FIG. 3.

The discharge passage 49, opens to a recess 51 in the cylinder 31, andterminates in a valve seat 52 for a discharge check valve 53 of anysuitable design. An elbow structure '54 is mounted on the top of thesecond stage cylinder 31 defining a transfer passage 55 communicatingthe recess 51 with a discharge passage 56 in the end wall 13, the jointbetween the elbow 54 and the end wall 13 being sealed by a suitableO-ring. The elbow structure 54 may include a web for supporting a bumper57 pro vided for limiting the opening movement of the discharge valve53. The discharge passage 56 opens to the upper periphery of the endwall 13; and communicates with a discharge housing 58 which may includean oil filtering device for the air discharge from the pump.

As indicated above, the described pump is an oil-sealed pump; and theannular space 22 surrounding the second stage cylinder 31 defines an oilreservoir, the housing being provided with a suitable filler opening notshown. A quantity of oil is maintained in this reservoir at a level,indicated in FIG. 3, such as to completely immerse the second stagecylinder 31 to assist in preventing leakage of atmospheric air into thesecond stage pumping chamber. This oil reservoir chamber 22 is subjectto atmospheric pressure; and, as best seen in FIG. 3, a controlled flowpassage 61 is provided in the cylinder 31 communieating the oilreservoir with the pumping chamber 32 adjacent to the discharge passage39. A controlled quantity of oil flows from the reservoir into thepumping chamber in response to differential pressure across the passage61. It will be seen that as each vane 35 passes the oil passage 61, thispassage will be communicated With the chamber defined between this vaneand the immediately following vane which is at a pressure lower thanatmospheric. Since the pressure Within the oil reservoir chamber isatmospheric, a certain quantity of oil will be forced into the pumpingchamber. Some of this oil will mix with the air; and this oil/ airmixture will be immediately forced out of the pumping chamber throughthe discharge valve 53 and be discharged to atmosphere.

As mentioned above, the discharge housing 58 may include a filter forremoving this oil from the discharged air; and the pump may furtherinclude a drainage line for draining the removed oil back to thereservoir chamber 22. A portion of the oil will coat the surfaces of therotor, vanes and cylinder bore of the second stage to performlubricating and scaling functions; and a portion of this oil willmigrate back to the first stage, to similarly lubricate and seal theparts for the first pumping stage.

As best seen in FIGS. 3 and 4, an inclined passage 62 is provided in thepartition 18, the lower end of this passage defining a port 63 openingto the annular space 21 and the upper end of this passage defining aport 64 opening to the second stage pumping chamber 32. As seen in FIG.3, the port 32 is adjacent to the second stage inlet port 48 but belowthe passage 47. This passage 62 communicates the annular space 21 withthe second stage inlet whereby, during operation of the pump, theannular space 21 is evacuated to the pressure of the second stage inlet(or first stage discharge) to define a vacuum jacket chamber for thefirst pumping stage, this chamber being maintained at a pressure betweenthe ultimate pressure of the first stage and atmospheric. This, ofcourse, results in a reduced leakage of air into the first stage,resulting in better pump performance in terms of the ultimate degree ofvacuum obtainable.

The vacuum jacket chamber 21 and the passage 62 provide an additionalfunction, namely to provide a chamber for receiving oil from the secondstage pumping chamber which might otherwise back up into the firstpumping stage or into the system being pumped when the vacuum pump isshut down. As already mentioned, it is not desirable that anysignificant amount of oil be permitted to contaminate the first or lowpressure stage of the pump, particularly when the oil contains entrainedair or moisture. In this regard, the location of the port 64 for thepassage 62 is important. When the pump is shut down, without the systembeing first vented to atmosphere, a pressure differential may existbetween the oil reservoir and the pump chamber between adjacent vanes cand a of the second stage rotor (as indicated in FIG. 3) which is incommunication with the oil passage 61 when the rotor stops. Because ofthe pressure differential, oil

will be forced through the passage 61 into this chamber;

and the second stage rotor 33 may then act as a motor being rotated in acounterclockwise direction. Without any provision for taking care ofthis oil carried in the chamber between the vanes c and a, this oilwould be communicated with the second stage inlet passage 47 when thevanes a passes the inlet port 48; and the lower pressure within theinlet passage would have the effect of sucking the oil out of thechamber between the vanes c and a and into the first stage pumpingchamber. It will be seen that this cannot occur, since the port 62 willbe uncovered by the vane a, well before the oil is raised to the levelof the inlet passage 47, to communicate with the chamber between thevanes c and a. The lesser pressure within the vacuum jacket chamber 21will result in a sucking of this oil into the vacuum jacket chamber; andvolume of the vacuum jacket chamber 21 is sufificient to accommodate allof the oil that may be pumped back in this manner until the pressuresare equalized.

Operation of the preferred embodiment In the above described pumpstructure, no special sealing agents or structures are used to seal theend surfaces of the stage cylinders and 31 to the respective closingsurfaces defined by the Walls 11 and 13 and the partition 18; and theproblems associated with such sealing agents or structures areeliminated. Despite the lack of such sealing means, leakage into thefirst stage is held to a minimum by the fact that the annular chamber 21surrounding the cylinder 25 is a vacuum jacket chamber maintained at thedischarge pressure of the first stage. Similarly, the annular chamber 22surrounding the second stage cylinder 31 is filled with oil to a levelto completely enclose the cylinder, thereby reducing leakage of air intothe second stage pumping chamber. Such oil that may leak into thepumping chamber along the surface of the end wall 13 and partition 18,is immediately pumped out by the rotor 33. The seal between the twochambers 22 and 21 is maintained by the pressure differential act-' ingon the O-ring 19. The atmospheric pressure existent in the oil reservoirchamber 22 acts laterally on the O- ring 19 urging the O-ring againstthe shoulder defined by the annular rib 20, to maintain an effectiveseal between the chambers 22 and 21. Should any oil leak into thechamber 21, this oil will immediately be pumped out through the passage62.

While in the above described preferred embodiment of the invention thepumping stages are rotary vane type pumping units, it will be understoodthat this particular type of pumping unit is not an essential topractice the invention and that other embodiments of the invention mayemploy other types of pumps such as eccentric piston type pumps. In theappended claims, reference is made to pumping stages including acylinder defining a pumping chamber and a rotor; and it will beunderstood that these terms as used in the claims are intended toinclude pumping stages of the rotary vane type, of the rotary 6 oreccentric piston type and of other equivalent pumping units.

In operation, the pump rotors are driven in a clockwise direction by theshaft 16, as viewed in FIGS. 2 and 3. The intake chamber 41 of the pumpis connected to the system to be evacuated by suitable tubulation, andair is withdrawn from the system by the first or low pressure pump stagethrough the passages 42, 43, and 44. The air so withdrawn is pumped bythe several chambers defined by the first stage cylinder 25, rotor 27,and vanes 29 to the first stage discharge passage 45 at higher pressure.This discharge air is then withdrawn by the second pumping stage throughthe passages 45, 46, 47, and 48, the air being pumped by the chambersdefined by the second stage cylinder 31, rotor 33, and vanes 35, anddischarged into the second stage discharge passage 49 at still higherpressure. This air is then discharged through the discharge check valve53 when sufficient pressure has been built up to lift the valve, whencethe air is discharged to atmosphere through the recess 51, passages 55and 56 and discharge housing 58.

Some of the oil which is admitted to the second pumping chamber throughthe oil passage 61 is discharged with the air; and some of the oil coatsthe internal parts of the second pumping stage to lubricate and seal therelatively movable parts. Some of this oil migrates back into the firstpumping stage to lubricate and seal the relatively movable parts of thisstage.

Since the annular jacket chamber 21 is communicated with the secondstage inlet port 48 by means of the passage 62, the pressure maintainedin the jacket chamber during operation of the pump is the same as theinlet pressure for the second pumping stage or the discharge pressurefor the first pumping stage. The space 21 then provides an insulationspace between the low pressure at the first stage inlet and the ambientatmospheric pressure at the exterior of the pump housing. This, ofcourse, reduces the leakage of air into the first stage pumping chamberto provide for a lower ultimate pressure which can be achieved by thepump.

As already explained, should the pump be shut down without first ventingto atmosphere, any oil in the system which may be transported to thesecond stage inlet passage 48, whereby it could be sucked back to thefirst vacuum stage, is sucked into the jacket chamber 21 through thepassage 62 becaue of the lower pressure existing in the chamber 21. Whenpump operation is resumed, this oil is sucked out of the chamber 21through the same passage 62 and carried by the second stage rotor to thedischarge passage 49.

What is claimed is:

1. A two stage oil-sealed vacuum pump comprising:

a housing defining first and second chambers;

a first low pressure pumping stage including a cylinder defining apumping chamber and a rotor; said first stage cylinder being mounted insaid first chamber to. define an annular space surrounding saidcylinder;

a second high pressure pumping stage including a cylinder defining apumping chamber and a rotor; said second stage cylinder being mounted insaid second chamber to define an annular space surrounding saidcylinder; said second chamber annular space defining an oil reservoir; acontrolled fiow passage communicating said oil reservoir with saidsecond stage pumping chamber;

passage means communicating the discharge port for said first pumpingstage to the inlet port for said second pumping stage;

passage means communicating said first chamber annular space with saidsecond stage pumping chamber whereby said annular space defines a vacuumjacket chamber for said first pumping stage; and said last-named passagemeans opening to said second stage pumping chamber at a port positionedto intercept oil flowing toward said second stage inlet port,

whereby said oil is withdrawn into said first chamber annular space toprevent contamination of said first stage pumping chamber.

2. The invention set forth in claim 1:

wherein said port for said last-named passage opening to said secondstage pumping chamber is below said passage means communicating theinlet port for said second pumping stage with the discharge port forsaid first pumping stage, whereby oil being carried toward saidfirst-named passage mean will be intercepted by said second-namedpassage means.

3. The invention set forth in claim 1:

including an internal partition in said housing defining said first andsecond chambers; said partition comprising a circular plate memberhaving a peripheral annular groove; an annular resilient sealing memberdisposed in said annular groove; said housing having an internal annularrib having an internal diameter only slightly larger than the diameterof said plate and defining a lateral shoulder adapted to be engaged bysaid resilient sealing member to provide a seal between the first andsecond chambers.

4. The invention set forth in claim 3:

wherein said housing comprises a cup-shaped member defining a first endwall thereof and peripheral side walls thereof, and a plate memberdefining the second end wall thereof; said annular rib being integralwith the housing side walls and disposed in a plane parallel to thehousing end walls; said annular rib shoulder facing said second endwall;

said first chamber being defined by first end wall and said partition;and said second chamber being defined by said partition and said secondend wall.

5. The invention set forth in claim 4:

wherein said first mentioned passage means communi cating said pumpingstages includes a passage through said partition; and said lastmentioned passage means communicating said vacuum jacket chamber andsaid second pumping stage comprising a passage through said partition.

6. The invention set forth in claim 4:

wherein said housing and walls define confronting parallel surfaces, andsaid partition defines opposing surfaces parallel to said end wallssurfaces;

said first pumping stage including a cylinder and rotor having parallelend walls which are dimensioned to be closely received within said firstchamber in sealing relation with the parallel wall surfaces thereof; andthe second pumping stage having a cylinder and rotor with parallel wallsdimensioned to be closely received within said second chamber in sealingrelation with the parallel wall surfaces thereof.

7. The invention set forth in claim 6:

wherein said first and second stage rotors are mounted on a common shaftpassing through said partition.

8. The invention set forth in claim 1:

wherein said pumping chambers are cylindrical; wherein said rotor arecylindrical and mounted eccentrical- 1y relative to the respectivepumping chambers to define a tangential seal line; and said rotorsincluding a plurality of radial slots accommodating sliding vanes forsealing engagement with the walls of the respective pumping chamber.

9. The invention set forth in claim 1:

wherein the rotors for said pumping stages are identical andinterchangeable.

References Cited UNITED STATES PATENTS 1,056,859 3/1913 Vernon 2301522,126,247 8/1938 Eppers 230l58 2,147,194 2/1939 Ells 230-152 X 2,150,1223/1939 Kollberg et al. 230152 2,824,687 2/1958 Osterkamp 2301582,877,947 3/1959 Wessling et al. 230-158 X 2,902,210 9/1959 Power 230158X 3,081,936 3/1963 Wessling 230-207 X 3,371,857 3/1968 Le Blanc 230152FOREIGN PATENTS 809,443 2/ 1959 Great Britain. 1,236,343 6/1960 France.

938,559 10/1963 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

W. J. KRAUSS, Assistant Examiner.

U.S. Cl. X.R.

